This invention relates to pressure gauges and, more particularly, to semiconductor strain gauges, such as for use in vehicles.
Operating conditions are determined in vehicles with the assistance of sensors. Pressure sensors can be useful to measure the pressure of fluids in vehicles. The sensed pressure can then be transmitted to an electronic display for the driver so that the driver will be alerted when the oil pressure is low and/or in need of further oil, such as motor oil, transmission fluid, etc. or when the carburetor needs more water or antifreeze, e.g. ethylene glycol. In more sophisticated vehicles, the sensed fluid pressure is transmitted to an onboard computer, computer chip, integrated circuit, or engine control unit which can adjust spark plug, timing, ignition (combustion), fuel injection rates, and other operating parameters to help optimize performance and efficiency of the engine and vehicle.
Diesel engines are very often used in trucks, locomotives and other vehicles. Original equipment manufacturers, distributors, and customers of diesel engines, as well as internal combustion engines, desire more efficient fuel delivery systems which minimize pollution in compliance with environmental regulations. Various high pressure direct diesel injection systems have been designed to atomize the fuel so that the fuel burns efficiently with less pollution. The use of pressure transducers in a closed control loop in association with an onboard computer, computer chip, integrated circuit, or engine control unit, can be helpful to improve vehicle performance and minimize harmful emission of pollutants.
Transducers are devices which function generally to convert an input of one form into an output of another form or magnitude. Pressure transducers convert pressure to voltage and are typically piezo-resistive. Pressure transducers are typically strain sensitive rather than displacement sensitive. Pressure transducers comprising semiconductor strain sensing devices are useful in pressure sensing applications, but have generally been previously limited to relatively low temperature applications. Semiconductor strain sensing devices exhibit non-linear impedance variation at elevated temperatures, such as at engine operating conditions. Conventional strain gauge resistors and their sensitivity to strain, usually change in such a manner as to preclude effective temperature compensation. As a result, many, if not most, semiconductor strain sensing devices have not been usable and effective at vehicle operating conditions.
There have been various attempts to provide temperature compensation for semiconductors strain sensors. A temperature compensation circuit has been suggested which comprises series connected PN junction diodes formed in an N epitaxial layer of silicon chips. Another suggestion has been to use a series of resistant strips connected to contact pads which terminate in other contact pairs that are orientated in a specific crystallographic direction. Strain gauges have been connected to a diaphragm to measure strain due to pressure. A further suggestion has been to use a monocrystalline silicon chip with a matrix silicon base material, a silicon diaphragm portion, and integral semiconductor strain sensing elements. It has been suggested to arrange the semiconductor strain sensing elements in a Wheatstone bridge circuit to sense the strain in a silicon diaphragm caused by fluid pressure. Remote terminals have also been suggested for interconnection between integral semiconductor strain sensing elements and circuitry external to the chip and in direct electrical connection to the matrix silicon base material to attempt to control the characteristics of the semiconductor strain sensing device in order to minimize degradation of the semiconductor material at high temperatures. Another suggestion has been to use silicon strain gauges bonded to a stainless steel diaphragm using high temperature glass fusion instead of epoxy bonding. These suggestions and prior semiconductor stains sensing devices have met with varying degrees of success.
High temperatures at which vehicle engines typically operate create high thermal expansion and high thermal stresses which often cause inaccurate pressure readings and measurements. As a result, the information electronically displayed to the driver is often inaccurate and misleading, and the pressure signal transmitted to the onboard vehicle computer, computer chip, integrated circuit, or engine control unit is often incorrect which can result in substandard and inefficient performance of the vehicle. With high engine operating temperatures, thermal stresses can also create electrical noise which can be much larger than the pressure signal. As a result, in some circumstances, the pressure signal may not even be displayed to the driver and transmitted to the onboard computer, computer chip, circuit board, or engine control unit. This situation becomes even more aggravated when different materials are interconnected, such as when a stainless steel diaphragm is bonded to silicon strain gauges by glass fusion. Furthermore, high temperatures can cause cracking, internal rearrangement, instability and even failure in a semiconductor strain sensing devices.
It is, therefore, desirable to provide an improved sensor which overcomes most, if not all, of the preceding problems.
An improved sensor is provided which can operate at high temperatures, such as the operating temperatures of diesel engines and internal combustion engines. Advantageously, the improved sensor is reliable, accurate, efficient, and effective at the operating temperature ranges of vehicles. Desirably, the user-friendly sensor is economical, convenient, simple to use, and safe.
The specially arranged sensor has at least one semiconductor and a detector for contacting a fluid. Desirably, the detector comprises a fluid responsive detector comprising a material which resists corrosion from the fluid. In the preferred form, the detector comprises a stainless steel diaphragm.
The specially arranged sensor also includes at least one gauge (gage) for measuring at least one characteristic of a fluid. The fluid can comprise a gas or a liquid, such as motor oil, diesel oil, transmission oil, brake fluid, gasoline, a petrochemical composition, such as antifreeze (ethylene glycol) etc., or water. Preferably, the gauge is operatively connected to the semiconductor and is advantageously positioned at a location to help minimize electrical effects of thermal stress during measuring. In the preferred form, the gauge comprises a vehicle gauge to measure at least one characteristic of a fluid in a vehicle, such as an automobile, sport utility vehicle (SUV), van, station wagon, truck, motorcycle, railway car (locomotive), airplane, ship, boat, barge, tractor, lift truck, backhoe, bulldozer, crane, and various road grading equipment. The gauge can be a stress gauge, pressure gauge, force gauge, or preferably a strain gauge. Desirably, the gauge is positioned at a location to help minimize the electrical effects of thermal stress and strain during operation of the vehicle and engine.
A support can be provided to hold and support the gauge. The support can comprise a die, a glass substrate, or a metal substrate formed of a metal such as aluminum, niobium, titanium, chromium, iron, bismuth, antimony, or steel. Preferably, a coupling is provided to secure the support to the diaphragm or other detector. In the preferred form, the support comprises a silicon-containing die and the coupling comprises glass frit providing fused glass.
The sensor can comprise a transducer with at least one semiconductor comprising one or more interconnects. The interconnects can comprise a silicon-containing semiconductor, such as an amorphous, microcrystalline, or polycrystalline silicon semiconductor, silicon carbon semiconductor, or silicon germanium semiconductor, or a copper indium diselinide (CIS) semiconductor, a copper indium gallium selenide (CIGS) semiconductor, or a gallium arsenide semiconductor.
In one form, the sensor includes an array of gauges comprising a group of interconnected resistors positioned in a special Wheatstone bridge arrangement on a single silicon-containing die to help minimize electric effects of thermal stress on the gauges during measuring and operation of the vehicle.
In another form, the sensor comprises a single transverse gauge which is specially arranged and positioned on a single silicon-containing die to help minimize electric effects of thermal stress on the transverse gauge during measuring and operation of the vehicle.
A more detailed explanation of the invention is provided in the following description and appended claims taken in conjunction with the accompanying drawings.